btrfs: Allow to specify compress method when defrag

Update defrag ioctl, so one can choose lzo or zlib when turning
on compression in defrag operation.

Changelog:

v1 -> v2
- Add incompability flag.
- Fix to check invalid compress type.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>

diff --cc fs/btrfs/ioctl.c
Simple merge

diff --cc fs/btrfs/ioctl.h
Simple merge